Optical glasses comprising aif3 having a varying partial dispersion

ABSTRACT

OPTICAL, FLUORINE-CONTAINING BARIUM SILICATE OR BARIUM BOROSILICATE GLASSES HAVING A VARYING PARTIAL DISPERSION, CHARACTERIZED IN THAT THEY CONSIST ESSENTIALLY OF: WT. PERCENT SIO2 15-45 B2O3 0-15 SIO2+B2O3 30-47 BAO 25-56 BAF2 0-10 BAO+BAF2 35-56 ALF3 3-18

Feb. 13, 1973 w. arrza 3,716,385

OPTICAL GLASSES COMPRISING AlF' HAVING A VARYING PARTIAL DISPERSION Filed April 6, 1970 2 Sheets-Sheet 1 FIG.7

Feb. 13, 1973 w. RITZE 3,716,385

OPTICAL GLASSES COMPRISING AlF HAVING A VARYING PARTIAL DISPERSION Filed April 6, 1970 2 Sheets-Sheet 2 f7 f7 pe c n 70.0

United States Patent (3 OPTICAL GLASSES COMPRISING AlF HAVING A VARYING PARTIAL DISPERSION Willy Ritze, Mainz-Mombach, Germany, assignor to .lENAer Glaswerk Schott & Gen., Mainz, Germany Filed Apr. 6, 1970, Ser. No. 25,871

Claims priority, application Germany, Apr. 11, 1969,

P 19 18 350.7 Int. Cl. C03c 3/00 U.S. Cl. 106-47 Q 3 Claims ABSTRACT OF THE DISCLOSURE Optical, fluorine-containing barium silicate or barium borosilicate glasses having a varying partial dispersion, characterized in that they consist essentially of:

Wt. percent g, 15-45 0-15 S +3 03 BaO 25-56 BaF 0-10 BaO-i-BaF 35-56 AlF 3-18 P 8 and P p:

Tip-Wile is greater than in the known silicate or borosilicate glasses, and which are preferably free of phosphoric acid.

The values P and P c are the relative partial dispersions.

Such glasses are important to the optical designer, because due to their varying partial dispersion he is in a position to correct the chromatic aberration of optical systems.

Glasses having a varying partial dispersion are already known. They are glasses which contain mainly phosphoric anhydride, in addition to boric anhydride, as glass formers, and at least one alkalineearth oxide, and can be melted with the addition of A1 0 ZnO, CdO, La O PbQ, and As O The phosphoric anhydride content in these glasses is relatively high, so that they are rather sensitive to weathering. Their optical properties are limited to the glass groups of phosphate crowns, phosphate heavy crowns and a portion of the heavy crowns. Some of them are very aggresive when molten, attacking the platinum crucibles, and their tendency to devitrify prevents continuous production on an industrial scale or melting vin large batches.

It is the object of the present invention to obtain glasses who'se composition permits their use as a material for optical elements in optical systems without presenting the difliculties in regard to melting and weathering which have been described above, and whose varying optical characteristics will cover a substantially broader range of glasses. v

This object is achieved according to the invention for optical, fluorine-containing barium silicate or barium borosilicate glasses having a varying partial dispersion in that they consist essentially of:

3,716,385 Patented Feb. 13, 1973 Wt. percent SiO 15-45 3 0 0-15 Slog-H8303 BaO 25-5-6 BaF 0-10 BaO-l-BaF -56 AlF 31-18 To establish a desired optical position in the range of the heavy and extra-heavy crowns and in the range of the barium flints, the following additional components can be introduced without substantially diminishing the varying partial dispersion:

z and/o1 Wt. percent U20 0 to 2 Eco and/or- MgO CaO 0 to 8 SrO PbO 0-2 A1 0 0-5 113203 Bi O 0-5 Zr0 0-9 TiO 0-14 ThO 0-18 Nb O 0-5 T3305 W0 0-3 AS203 and/o1 Sbg03 02 the sum of these components not exceeding 25% by weight, and being preferably less than 15% by weight.

An additional fluorine content up to 3% by weight can be put into the melt as, e.g. alkaline earth fluoride (e.g. BeF, CaF MgF or in other form (e.g., as an alkaline earth alkali silicofluoride).

The n values of the glasses according to the invention are greater than 1.54 and the v values are less than 66.

Glasses of the aforementioned quantitative analysis, and further qualified so as to range in composition as follows have proven to be especially valuable:

the sum of the principal components, SiO B 0 B210, BaF; and AIR being greater than 97% by weight.

Glasses having compositions based on these data can be melted in the large platinum or ceramic crucibles and preferably in continuous melting units, to produce glasses of good optical quality. Their chemical resistance is better than that of the phosphate glasses.

On account of the incorporation of TiO +ZrO the resistance of these glasses according to the invention to acids is better than that of the known silicate or borosilicate glasses having a high barium content.

Examples of the new glasses are listed in the table which follows.

is plotted against the Abbe number v 5 References Cited UNITED STATES PATENTS Sun 106-47 Q Nishimoto et a1. 10652 Armistead 10647 Q Getfcken 106-47 Q 6 FOREIGN PATENTS 1,056,335 4/1959 Germany 10647 Q 570,108 2/ 1959 Canada 10647 Q 5 HYLAND BIZOT, Primary Examiner W. R. SATTERFIELD, Assistant Examiner 

